Internal combustion engines (ICE), in particular the well-known Otto-cycle or “four stroke” engine) are fueled with a combustible mixture of fuel (e.g. gasoline) and air. Perhaps two of the most undesirable characteristics of an ICE are the relatively low efficiency and relatively high contaminant emission exhibited by these engines. This inefficient utilization of the fuel, detracts from control of engine power output, and undesirable, and even harmful emissions.
For purposes of the present disclosure, the four strokes of the engine comprise an intake stroke, a compression stroke, a power stroke and an exhaust stroke. The cycle begins when the piston of the engine is at top dead center (TDC). Herein, the four stroke cycle is deemed to commence when the rotational position of the crankshaft (which moves with the piston through its strokes) is such that the piston is at TDC. All references to rotational positions of the piston are based upon the degrees of rotation of the crankshaft from the starting TDC of the piston. For example, 10 degrees before TDC refers to the rotational position of the crankshaft being 10 degrees before the commencement of a power stroke of the engine cycle.
Probably, the most common of the many attempts of prior art devices and methods for attacking the problems associated with ICEs is utilization of a flame front initiated outside the normal combustion chamber of an ICE and thereafter propagated into the main combustion chamber wherein such flame front ignites the usual charge of air/fuel mixture (herein at times A/F or A/F mixture) disposed within the combustion chamber. Whereas some of these attempts have achieved at least limited desired results, none of such attempts are known to have economically or otherwise effectively provided both the sought after increase in efficiency and simultaneous reduction of environmentally unfriendly exhaust emissions associated with ICEs.
Currently, in the ICE industry, there are two aspects of the industry which in part tend to require different possible means for enhancement of the efficiency of the ICE plus minimization of the exhaust emissions from the engine. The first such aspect relates to the number of ICEs currently in use and which employ carburetor systems and the second aspect relates to the more recent and currently expanding market for ICEs employing engine control modules (ECM) (which control spark timing, fuel injection, etc).
In the prior art the concept of employing flame front(s) initiated externally of the main combustion chamber and propagated into the main combustion chamber, for ignition of the air/fuel mixture within the main combustion chamber has been somewhat heavily pursued. This concept is more or less compatible with either carburetor or fuel injection systems, but its uses are expanding primarily into those engines employing fuel injection for introduction of a quantity of a air/fuel mixture into the engine combustion chamber once per cycle of the engine through its intake stroke, compression stroke, power stroke and exhaust stroke of the piston.
In those ICEs which employ a carburetor for the introduction of an A/F mixture into the combustion chamber of the engine, the A/F mixture disposed within the combustion chamber is ignited by means of a spark plug which projects into the combustion chamber. It has been proposed in the prior art to employ a relatively lean A/F mixture as an aid toward reduction of undesirable emission products. Heretofore, mere incorporation of a flame front pre-combustion system in a carburetored ICE has failed to be economically, operationally or otherwise suitably beneficial.
ICEs which are controlled by an ECM, for example, commonly utilize stoichiometric A/F mixtures for enhanced utilization of the fuel employed to operate the engine. These EMC controlled systems tend to generate excessive nitrogen-containing emission products. The well-known “three-way catalyst” system has been found effective to preclude such nitrogen-containing emission products from entering the atmosphere; however, this catalyst system is ineffective in combination with carburetored ICEs.
air/fuel mixture is one of the more important principles of internal combustion engine operation. For gasoline, the stoichiometric air/fuel ratio is 14.7:1. That is, 1 unit of fuel mass is consumed for every 14.7 units of air mass that are drawn into the engine. The stoichiometric is neither most fuel efficient nor delivers the most power, it is a compromise.
The stoichiometric ratio usually is the least polluting, because the catalytic converter can most easily remove pollutants at such a ratio. The stoichmetric mode is most often used during cruising and light acceleration.
For optimum power, a 12.7:1 (slightly fuel-rich) air/fuel ratio should be used. However, it is not very fuel efficient, it can foul spark plugs, and is polluting (the catalytic converter is outside its optimum range, and very polluting unburned hydrocarbons are released). Modern cars usually only use this mode (called fuel enrichment mode) under hard acceleration.
For maximum fuel economy, a 16.1 (fuel-lean) air/fuel ratio should be used. However, the lack of extra fuel to cool the engine results in hot, less dense intake air, reducing power. Also, the extra heat puts stress on engine parts, and increases octane requirement. Although less polluting than fuel-rich, fuel-lean produces large amounts of nitrogen oxides, as well as putting the catalytic converter out of its range. Lean mixtures are generally not used on modern, pollution-controlled vehicles.
These factors have led to the practice of developing an Electronic Control Module for internal combustion engines wherein various operational factors of the engine are monitored and employed to provide to the IEC the most fuel efficient, minimum contaminating and otherwise desirable air/fuel ratio which provides the maximum torque at any one of a range of engine rpms which are representative of the anticipated operating conditions of the engine (e.g. low rpms at idle speeds to high rpms at higher or more torque-demanding operating conditions.) This concept “torque control” has led to the use of operation maps developed for a given engine. Such maps take into consideration the timing of the initiation of the spark ignition of the air/fuel mixture disposed within the combustion chamber of the engine (before TDC of the crankshaft) as will maximize the torque developed at any given combination of air/fuel intake at any given rpm of the engine. That is, these maps are based upon torque output values. Inasmuch as the torque values desired at different rpms of the engine, the timing of the ignition of the combustion of the air/fuel mixture varies considerably between idle speeds and higher rpm speeds. Such maps are developed for a given engine employing a very large number of test runs of the engine at each combination of rpms and air flow into the combustion chamber of the engine. These maps, therefore, are specific for a given engine. Most commonly the operational map for a given engine is available from the manufacturer of the engine. However, one skilled in the art can develop an operational map for a given engine by following the multiple testing procedures referred to above. These operational maps have generally become the “standard” for ICEs, particularly where the ICE is controlled by an ECM.
The present inventor has found, however, that enhancement of the efficiency of multiple aspects of the operation of an ICE, whether controlled by an ECM or a carburetor, can be materially enhanced. In accordance with the present invention, such enhancement is accomplished through the use of a flame front type pre-combustion system which effects commencement of the ignition of the fuel/air mixture disposed within the combustion chamber of an ICE at a time which is about 5 degrees later than the ignition time dictated by a prior art operational map. This retardation of the timing of ignition of the fuel/air mixture has been found possible over substantially all anticipated combinations of engine speed and rate of air flow into the combustion chamber of the engine. In certain combinations of engine speed and the lower air flow rates, the retardation of the timing may exceed 5 degrees, thereby further enhancing the efficiency of operation of the engine at such lower speed and air flow rate combinations.